'watchful' originates from the Old English word 'wæccan,' where 'wæc-' meant 'to be awake or alert.'

'wæccan' transformed into the Middle English word 'wacchen,' and eventually became the modern English word 'watchful.'

Initially, it meant 'to be awake or alert,' but over time it evolved into its current meaning of 'being alert and vigilant.'